1. Field of the Invention
The invention relates in general to short term dust sampling and, in particular, to a personal sampling apparatus using a low flow-rate gas sample pump and providing differential pressure measurements across a collection filter in a detector tube device indicative of dust mass.
2. Description of the Related Art
Current methods of airborne dust sampling and detection require expensive instantaneous and short term monitors or gravimetric filters. Present gravimetric dust filtering techniques are cumbersome. When gravimetric filters are used, careful pre-weighing and post-weighing is required to determine the dust mass collected during a sampling period. The determined average dust exposure to workers during their shift from the dust collected is thus identified as the total dust or respirable dust, if sampled through a 10 millimeter cyclone.
A number of institutions and laboratories are engaged in the general area of aerosol measuring research. A wide variety of techniques have been developed for collecting dust sample fractions including the use of weight, volume and time measurements for determinations of dust mass per cubic meter exposure. Typical techniques employed in industry include the use of a photometer for measuring the scattering of light, beta particle detection wherein dust mass attenuates a beta source to measure concentrated dust deposits, crystal frequency oscillator variations proportional to dust deposits, and the like. A pressure drop has been used to detect filter loading generally and for selecting and designing filters.
U.S. Pat. No. 4,586,389 to Vincent, et al., for xe2x80x9cDust Detectionxe2x80x9d issued May 6, 1986 discloses a portable aerosol dust spectrometer having an inlet section sampler entry with efficiency for airborne dust approximating that of human inhalation with a main collection stage which is a cascade impactor. Such cascade impactors classify particles of dust and collect fractions onto a number of collection surfaces for defined dust particle size selections. A pump draws air or gas through the apparatus and yields fractions of dust for further weight, volume and time studies. U.S. Pat. No. 4,740,220 to Mark, et al., for xe2x80x9cDust Detectionxe2x80x9d issued Apr. 26, 1988 similarly discloses a dust spectrometer for collecting various size fractions of dust for subsequent analysis to determine exposure, wherein the described impactor is designed to be worn by a person and powered by an external pump. U.S. Pat. No. 4,827,779 to Marple, et al., for xe2x80x9cCartridge Personal Sampling Impactor,xe2x80x9d also collects dust for subsequent analysis using a compact impactor design.
U.S. Pat. No. 5,223,439 to Rolle for xe2x80x9cRadon Daughter Dosimeterxe2x80x9d issued Jun. 29, 1993 provides a radon daughter dosimeter using a cyclone and a radiation detector spaced from a filter, wherein the filter is arranged to filter dust and aerosol particles in air or gas from the outlet of the cyclone. U.S. Pat. No. 3,558,884 to Leningradskee, et al., issued Jan. 26, 1971 discloses collecting dust on a filter and using the difference in penetration of beta radioactive decay before and after disposition as a method of determining dust mass deposited on the filter. U.S. Pat. No. 5,056,355 to Hepher, et al., for xe2x80x9cDust Monitors and Dust Monitoring,xe2x80x9d issued Oct. 15, 1991 relates to the use a piezo-electric crystal as a dust detector wherein dust impacting on the surface of the crystal changes the vibrational frequency in proportion to the dust mass deposited upon the crystal for measuring the dust collected. U.S. Pat. No. 5,514,562 to Saugmann, et al., for xe2x80x9cMethod and an Apparatus for Currently Measuring the Presence of Traces of an Undesirable Substance in Air,xe2x80x9d issued May 7, 1996 uses chemical reactivity to effect a change in a solution for optical electronic detection using a photodiode and an opposing spectrophotometer.
A number of gas detection techniques are widely known in the art including sorbent tube applications with low flow-rate gas sampling pumps using gas detector tubes packed with colorometric chemicals which react with gas drawn into the gas detector tube with the sampling pump to display a colorant which identifies the particular gas sample. U.S. Pat. No. 4,254,657 to Leichnitz, et al., for xe2x80x9cGas Detector and Meter Employing Indicator Tubesxe2x80x9d issued Mar. 10, 1981 discloses a gas detecting and measuring device with which the gas or air to be examined is taken into a testing or measuring vessel such as an indicator tube by means of a feed system including a suction pump and pressure gauge for pumping the gas to be tested through a connecting line. U.S. Pat. No. 3,861,216 to Wachter, et al., for xe2x80x9cMeasuring Device Having Means for Applying a Selected Pressure to a Pressured Vessel,xe2x80x9d issued Jan. 21, 1975 and U.S. Pat. No. 3,861,217 to Rabenecker, et al., for xe2x80x9cGas Detection Device,xe2x80x9d issued Jan. 21, 1975 relate to methods of using gas pressure to draw a sample into a gas collection device.
A need exists for an inexpensive short term determination of personal dust exposure to aid in assuring the respiratory health of workers, which eliminates the need for the use of the costly, tedious and cumbersome techniques employed presently. Moreover, the mining industry is in need of a simple and inexpensive dust dosimeter, which also may have greater application in general industry where dust is a concern. It would be particularly advantageous to provide a standard apparatus for dust detecting device and real time dust dosimetry to aid in assessing dust exposure and assure the respiratory health of workers that work in environments where dust is a concern.
The dust detector tube device disclosed herein provides a personal sampling method and apparatus for real time respirable dust dosimetry for dust exposure assessment, having commercial usefulness enhanced by possible distribution through close relation to the established gas detector tubes employed today for gas detection. The present gas detection techniques of using gas sampling pumps and gas detection tubes has made small constant flow and constant pressure pumps widely available for sorbent tube applications. By standardizing a dust detector tube with other types of gas detector tubes, the cost and need for separate dust measuring devices is eliminated since the same pump can be used advantageously to measure both dust and gas.
The dust detection tube for dust exposure assessment aids in assuring respiratory health. An embodiment uses a low flow-rate gas sampling pump with a pressure transducer for differential pressure measurements across a glass fiber collection filter in a disposable detector tube or dust detecting device coupled to the pump inlet. The dust detecting device includes an elongated tubular element having the filter positioned between proximal and distal ends of the tube for trapping dust mass. A pressure transducer at the proximal end measures the pressure from the flow of gas. The pump draws the flow of gas through the dust detecting device from the distal end towards the proximal end trapping the dust mass at the filter.
Briefly summarized, the present invention relates to an apparatus for real time dust dosimetry using the sampling pump having inlet port coupled to the dust detecting device or tube for detecting dust mass exposure using differential pressure measurements. The tube is elongated with the collection filter positioned therein for trapping dust mass. The dust detecting device coupled to the pump draws the flow of gas therethrough and traps selected dust mass at the collection filter. Differential pressure between the pump side of the collection filter and the atmosphere is indicative of the cumulative dust mass trapped.
It is an object of the present invention to provide a dust detector tube device that overcomes the disadvantages and problems of prior art dust dosimetry apparatus.
It is another object of the invention to provide a dust detecting tube for real time dust dosimetry.
It is a further object of the invention to provide an apparatus and a method of real time dust dosimetry.
Other objects and advantages of the present invention will become apparent to one of ordinary skill in the art, upon a perusal of the following specification and claims in light of the accompanying drawings.